1. Field of the Invention
The present invention relates to an internal combustion engine including: a first injector for injecting fuel into an intake port or a combustion chamber; a second injector for injecting the fuel into the combustion chamber following the injection of the fuel by the first injector; and a spark plug for igniting an air-fuel mixture within the combustion chamber, and also relates to a method of such fuel injection.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2003-49651 (JP '651) discloses a direct fuel-injection type engine that includes a spark plug and a fuel injection valve for directly injecting fuel into a combustion chamber The engine disclosed by JP '651 conducts a first fuel injection to produce a relatively lean air-fuel mixture within the combustion chamber and a second fuel injection to produce a relatively rich air-fuel mixture around the spark plug. In the engine disclosed by JP '651, a first combustion is conducted by spark-igniting the air-fuel mixture produced by the second fuel injection, and a second combustion is conducted by compressive hypergolic ignition of the air-fuel mixture surrounding the spark plug due to a rise in temperature and pressure within the combustion chamber caused by the first combustion.
However, in the engine disclosed by JP '651, the air-fuel ratio of the air-fuel mixture produced by the first fuel injection is not always appropriate. Therefore, when the operating load is increased, an undesired knocking result occurs due to the enriched air-fuel ratio. Also, when the operating load is decreased, an undesired misfire result occurs due to the lean air-fuel ratio without the compressive hypergolic ignition occurring. Thus, the operating range of the engine disclosed by JP '651 is limited, resulting in the possibility of an insufficient decrease in the amount of discharged NOx and an insufficient decrease in the amount of consumed fuel occurring.